Project Summary Based on estimates derived from large consortium studies, HIV-associated neurocognitive disorders (HAND) affects between 22-84% of infected individuals at any one time. The vast majority of HAND diagnoses are mild, and are termed Asymptomatic Neurocognitive Impairment (ANI) in the most recent research diagnostic criteria. As many as 70% of those diagnosed with HAND have ANI, according to data from the CHARTER study. Yet some argue that ANI is over diagnosed, citing the fact that when the diagnostic criteria are applied to otherwise healthy, uninfected individuals, there is a very high rate of false-positive diagnoses. Another likely reason for the overestimated prevalence of ANI is suboptimal effort. That is, individuals enrolled in research studies from which prevalence rates are derived may not put forth sufficient effort on neurocognitive testing, thereby inflating estimates of mild HAND prevalence. Preliminary data from the Multicenter AIDS Cohort Study (MACS), the largest HIV study incorporating neurocognitive measures, indicates that over 50% of MACS participants who recently completed comprehensive neurocognitive testing reported suboptimal effort. The most common reasons being fatigued/tired, having poor concentration/distraction, and ?other?. Furthermore, there was an ordinal relationship between effort level and HAND severity, indicating that those with the poorest effort have the highest rates of ANI diagnosis. The preliminary data also allowed for identification of predictors of suboptimal effort, including low education and unemployment. These preliminary findings are extremely important for the future study of HAND. They suggest not only that rates of HAND are inflated due to poor effort among research participants, but also that there are specific causes for, and predictors of, suboptimal effort that can be addressed. In the proposed study, we will further explore suboptimal effort in the MACS. The results may lead to adjustments in HAND prevalence estimates and establishing methods for optimizing effort in research studies.